Steps of Excretion

Where does the first step of excretion occur?

In the renal artery

What does the renal artery do?

brings blood to the kidney to be filtered

What are some examples of things that they kidney filters out?

oxygen, water, urea, salts, glucose, amino acid

What is the second step of excretion?

Ultrafiltration

Ultrafiltration

removes solutes from blood

Where do the small substances move from and to where?

from the glomerulus to the renal capsule

Give some substances that are small enough to move through ultrafiltration

glucose, water, ions, salt, amino acids, nitrogenous wastes

Name two substances too big to move with ultrafiltration. What happens to them?

Blood cells and proteins which stays in the blood vessel

What are four characteristics that allow the glomerulus to aid in ultrafiltration?

high blood pressure, fenestrated membranes, basement membrane, podocytes

What is the effect of high blood pressure in the glomerulus?

forces particles through the membrane

Fenestrated membrane

have pores in the membranes

What is the purpose of the basement membrane in the glomerulus?

protein gel, acts as a filter, only small particles get through

What are podocytes and its purpose in the glomerulus?

cells that wrap around capillaries and provide support

What is the third step of excretion?

selective reabsorption

Selection reabsorption

body reabsorbs what it needs back into the blood vessels that wrap around the nephron

Where does selective reabsorption occur?

occurs in convoluted tubules and loop of Henle

How does the proximal tubule help in selective reabsorption?

microvilli increase surface area, many mitochondria for active transport

What two processes are used to reabsorb substances in the proximal tubule?

active transport and osmosis

What does active transport collect with reabsorption?

glucose (cotransport), amino acids, sodium ions, chloride ions

What does osmosis collect for reabsorption?

some water

What does the descending limb of the loop of Henle do?

reabsorbs water (by osmosis)

What does the ascending limb of the loop of Henle do? (3)

• maintains high osmotic concentrations (hypertonic) in the medulla

• facilitates water reabsorption in the collecting ducts

• reabsorbs Na and Cl ions by active transport

Is the ascending limb permeable to water?

No, it’s impermeable

What affects the loop length of the loop of Henle?

the amount of water that is reabsorbed

Longer length of the loop of Henle means…

conserves more water, wider medulla

Name an organism that has a longer loop of Henle

desert kangaroo rat

Shorter length of the loop of Henle means…

conserve less water, narrower medulla

Name an example of an organism with a shorter loop of Henle

river otter

What does the distal tubule do?

reabsorbs some ions if needed (i.e. Na⁺, Cl^-, and Ca⁺²)

What is the fourth step of excretion?

secretion

What happens during secretion

more chemicals are added from blood into nephron filtrate

What are some examples of chemicals added into the nephron filtrate?

Ions (H⁺, K⁺) and drug residue (often in distal tubule)

What is the fifth step of excretion?

Urine development

How is urine made?

filtrate becomes urine in the collecting duct

What can affect the concentration of urine?

water reabsorption by aquaporins

Where does the sixth step of excretion occur?

Renal vein

What occurs in the renal vein during the sixth step?

blood exits the kidney carrying what was too big to be filtered, what was reabsorbed, and CO₂ from ATP production